Hand pumps containing hydraulic fluid are often used to pressurize hydraulic piston/cylinder assemblies in order to exert high forces on objects by pumping a handle on the pump. A piston/cylinder assembly can be attached to the hand pump to lift heavy objects, such as a vehicle. The hand pump includes an outlet that is connected to an inlet of the piston/cylinder assembly in order to transfer the hydraulic fluid from the pump to the piston/cylinder assembly. In order to lift the vehicle, the piston/cylinder assembly is placed under a frame of the vehicle and an operator operates the handle to pump the fluid under pressure. The pumping moves hydraulic fluid from a reservoir to the pump's outlet and finally to the piston/cylinder assembly. As the operator pumps, the pressure in the piston/cylinder assembly increases and thus, the piston/cylinder assembly will extend and be able to raise the vehicle.
One type of hand pump is the two-stage hand pump, which moves the hydraulic fluid in two stages. The two-stage hand pump may have a piston cylinder that includes a low and high pressure portions. In the first stage, both the low and high pressure portions contribute to moving the hydraulic fluid from the reservoir to the pump's outlet and to the piston/cylinder assembly. In the second stage, only the high pressure portion contributes to moving the hydraulic fluid to the piston/cylinder assembly while the low pressure portion returns the hydraulic fluid back to the reservoir. During the second stage, the conventional hand pump utilizes a direct-acting relief valve to relieve the low pressure portion and return fluid back to the reservoir. However, the use of the direct-acting relief valve is inefficient because during the second stage, every stroke of the hand pump requires additional effort by the operator to open the relief valve. Additionally, using a direct-acting relief valve can decrease the oil volume and pressure that can be delivered in the first stage.
A conventional two-stage pump limits the distance between the pivot point in the handle and the piston. Because the distance is limited, the mechanical advantage of the handle is not as great and the handle requires more effort to pump. Additionally, the conventional two-stage hand pump also includes a tie rod nut that protrudes from the housing. Because the tie rod is on the outside surface, the overall length of the pump is increased without increasing the oil reservoir capacity of the pump. Further, conventional hand pumps may or may not have a locking device to lock down the handle. Some handle locks may be awkward to use or prone to damage or misplacement because they are not integral with the pump. Accordingly, it is desirable to provide a hand pump that requires little or no additional pumping force during the second stage in order to return the first stage fluid back to the reservoir. It is also desirable to have a handle with a wider range of movement and to include a handle lock that is easy to use and integral to the pump construction so it is protected from damage and will not be lost. Additionally, it is desirable to have a tie rod nut that does not protrude from the rest of the pump so as to minimize the length of the pump while maximizing the capacity of the pump reservoir.